Detection system

ABSTRACT

A detector is disclosed for detecting the presence of substances that form ions in liquids, comprising a porous, non-conducting wicking material which is electrically connected to a power supply and a current or resistance detecting device.

[111 3,751,969 1451 Aug. 14, 1973 United States Patent 11 1 Schrock [5 DETECTION SYSTEM 2,992,170 7/1961 Robinson.................... 2,806,991 9/1957 White [75] Inventor. Steven L. Schrock, Madrson, Pa. 2,760.1 52 8/1956 Katz ct alm [73] Assignee: Westinghouse Electric Corporation, 19951870 3/1935 Stone Pittsburgh Pa 2,1 13,063 4/1938 Stryker et al.

2,953,441 9/1960 Aug. 17, 1970 [22] Filed:

Primary Examiner-James J. Gill Att0rney-A. T. Stratton and Z. L. Dermer [2]] Appl. No.: 64,360

[52] US. 73/23, 23/254 E, 324/29,

340/237 @0111 27/00 73/23, 27,73, 26, 4 E 255 E, 254 A detector 15 disclosed for detectm R; 338/34; 340/237 ABSTRACT [51] In1t.Cl. [58] Field of Search g the presence of 73/29; 23/232 E, 25 204/196 R, l T; 324/29, 30

substances that form ions in liquids, comprising a porous, non-conducting wicking material which is electrie r r 0 t n e r r u c a m a .w D. D. u s a we 0k v m n d we m 8 d n 0e m Wm ab cs S T N E T A t P m m mT .mS D E T .l N U 1 6 5 1,475,000 11/1923 Cooper et al. 314/30 R X 7 Claims, 1 Drawing Figure IIlljr 11,11 111 lI/f/lA/fl/IlId/l PATENIEU M19] 4373 INVENTOR Steven L. Schrock BY; pg?

WITNESSES.

ATTORNEY DETECTION SYSTEM BACKGROUND OF THE INVENTION This invention pertains in general to a detection sys tern that detects the presence of substances that form ions in liquids and more particularly to a sodium oxide smoke detector for detecting sodium leaks in liquid sodium systems.

High temperature liquid sodium will be used as the coolant in fast breeder reactors. Numerous developmental tests are being conducted at this time in liquid sodium systems to qualify components for the fast breeder reactor. Since sodium reacts with air, releasing sodium oxide smoke, a hygroscopic solid, at room temperature, the rapid shutdown of a sodium system in the event of a rupture in the containment tube is imperative. Current practice is to use photoelectric cells in the cooling air duct work to detect the smoke. However, these devices have several disadvantages. For instance, most leaks are initially so small that dilution of the smoke prevents detection by the cell. Also, since the operation of the cell depends on smoke breaking a beam of light, a burned-out light bulb can cause an expensive shut-down. Also, these cells need to be cleaned frequently to prevent a shut-down due to dust accumulation. In addition to the photocells, the prior art has employed ionization gauges for smoke detection. These devices are not selective to sodium smoke, however, and are not capable of operating at the elevated temperatures sometimes encountered in the duct work from sodium systems.

SUMMARY OF THE INVENTION This invention overcomes the difficulties of the prior art by utilizing a porous non-conducting wicking material which is generally disposed within the air duct work of the sodium system. The wicking material is partially immersed in water and is provided with electrical contacts at each end. One such contact is serially connected to a low voltage power supply and a current or resistance detecting device such as an ammeter or ohmmeter.

Since ordinary tap water is not a good conductor, the electrical resistance would be high and current flow in the circuit would be very low. However, when sodium oxide is present in the air flowing past the wicking material, due to its hygroscopic properties, it is immediately absorbed by the water in the wick and ionized to form a conducting solution. Either the subsequent rise in current or drop in resistance could be detected and used'as the signal for system shut-down. This device would be selective for a substance which reacts with the liquid saturating the wick to form a highly conducting solution, i.e., sodium oxide, carbon dioxide, or hy drogen chloride. It would not be affected by dust or other foreign material. If a battery is used as a back-up power supply, the system will also be independent of an outside power failure.

The devices utilized by the prior art for detecting sodium oxide smoke measured the amount of smoke at an instant of time. The present invention has an advantage over that characteristic of the prior art inasmuch as it measures the cumulative effect of the ionizable material detected, since the latter material cannot escape once it is absorbed by and reacts with the liquid in the wicking material. Therefore, very small leaks can be detected with this device while they might have escaped notice under prior art detection devices.

As previously mentioned, this device can also be used for detecting the presence of carbon dioxide. The carbon dioxide will react with the water in the wick to form a conducting solution of carbonic acid (CO H O H CO and thus reduce the resistance in the wick to enable detection. Similarly this device can be used to detect the presence of any substances that react with a relatively non-conducting material to produce an electrically conducting medium.

BREIF DESCRIPTION OF THE DRAWING For a better understanding of the invention, reference may be had to the preferred embodiment, exemplary of the invention, shown in the accompanying drawing, in which:

The FIGURE is a schematic diagram with parts broken away and is illustrative of a sodium oxide detection device disposed within the air duct work of a sodium system and is representative of the preferred embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the exemplary embodiment illustrated in the FIGURE, it will be observed that this device comprises a porous, non-conducting wicking material 12, such as alumina or asbestos, which is generally disposed within the air duct work 10 of a sodium system. The wicking material 12 is electrically connected at one end 22 to one terminal of a relatively low voltage supply 14. The other terminal of the voltage supply 14 is electrically connected to a current or resistance detecting device 16, such as an ammeter or ohmmeter. The detecting device 16 is electrically connected to the other end 24 of the wicking material 12 so as to complete the series circuit 26.

It will be observed from the illustration that the wicking material 12 is partially immersed within a water reservoir 18 which is continuously supplied with water through an inlet 20. Since ordinary tap water is not a good conductor, the electrical resistance is high and the current flow in the circuit will be very low. However, when sodium oxide is present in the air flowing past the wicking material 112, it is immediately absorbed, by virtue of its hygroscopic properties, by the water in the wicking material 12 and ionizes to form a conducting solution, lowering the resistance between the wick ends 22 and 24. Either the subsequent rise in current or drop in resistance is detected by the detecting device 116 and is used as the signal for system shutdown. The size of the voltage supply 14 depends mainly upon the resistance of the wicking material 12 and the sensitivity of the detecting device 16.

This device is operative only with substances which react with the liquid saturating the wicking material to fonn a highly conducting solution, i.e., sodium oxide. It will not be affected by dust or other foreign material.

If a battery is used as a back-up power supply, the system is independent of an outside power failure.

The sodium oxide smoke detection devices of the prior art, measured the amount of smoke at any instant of time. The present device will have a cumulative effect since the sodium oxide cannot escape once it is absorbed by and reacts with the water in the wicking material. Therefore, even very small leaks will be detected with this device. Thus, this invention provides a more dependable device for the shut-down of sodium systems, in the event of an emergency situation such as the rupture of a containment tube, by: (l) detecting small amounts of sodium oxide smoke; (2) operating for long periods of time with little or no maintainence; and (3) by being selective for sodium oxide smoke and not being affected by other foreign materials such as dust or organic vapors.

What has been shown and described as the preferred embodiment of this invention is merely one application of the detection system to a liquid sodium system. This invention has a broader application inasmuch as it is capable of detecting the presence of any gas that reacts with a relatively non-conducting material to produce an electrically conducting medium.

I claim as my invention:

1. An on-line detection system for continuously monitoring a fluid stream within an enclosed fluid duct to detect the presence within the fluid stream of a substance that forms ions in liquids comprising:

a porous, electrically non-conducting wicking material at least partially disposed within the interior of the fluid duct and continuously exposed to the fluid stream therein, said wicking material being wetted with a relatively non-conducting medium that characteristically forms a relatively conducting medium by cumulatively collecting ions associated with the substance being detected when in fluid communication therewith so as to be responsive to even minute quantities thereof;

a plurality of electrical contacts provided on at least two spaced points along said non-conducting wick; and

means associated with said contacts for detecting a change in electrical resistance within said wick along a path defined by the two spaced point locations of said contacts.

2. The detection system of claim 1 wherein said wicking material extends through the duct to the exterior thereof, the portion of said wick exterior of the duct being at least partially immersed in a reservoir of said non-conducting medium.

3. The detection system of claim 1 wherein said wicking material is selected from the group consisting of alumina (A1 0 and asbestos.

4. The detection system of claim 1 wherein said nonconducting medium comprises water.

5. The detection system of claim 1 wherein said resistance detecting means comprises a power supply and a device responsive to changes in resistance within said wicking material to provide an output representative thereof, said power supply and said device being serially connected to said respective electrical contacts.

6. The detection system of claim 2 wherein said reservoir is provided with inlet means to maintain the level of said non-conducting medium.

7. The detection system of claim 2 wherein the fluid duct is hermetically sealed and the wick penetration is impermeable to the fluid stream so as to completely confine the fluid stream within the fluid duct. 

1. An on-line detection system for continuously monitoring a fluid stream within an enclosed fluid duct to detect the presence within the fluid stream of a substance that forms ions in liquids comprising: a porous, electrically non-conducting wicking material at least partially disposed within the interior of the fluid duct and continuously exposed to the fluid stream therein, said wicking material being wetted with a relatively non-conducting medium that characteristically forms a relatively conducting medium by cumulatively collecting ions associated with the substance being detected when in fluid communication therewith so as to be responsive to even minute quantities thereof; a plurality of electrical contacts provided on at least two spaced points along said non-conducting wick; and means associated with said contacts for detecting a change in electrical resistance within said wick along a path defined by the two spaced point locations of said contacts.
 2. The detection system of claim 1 wherein said wicking material extends through the duct to the exterior thereof, the portion of said wick exterior of the duct being at least partially immersed in a reservoir of said non-conducting medium.
 3. The detection system of claim 1 wherein said wicking material is selected from the group consisting of alumina (Al2O3) and asbestos.
 4. The detection system of claim 1 wherein said non-conducting medium comprises water.
 5. The detection system of claim 1 wherein said resistance detecting means comprises a power supply and a device responsive to changes in resistance within said wicking material to provide an output representative thereof, said power supply and said device being serially connected to said respective electrical contacts.
 6. The detection system of claim 2 wherein said reservoir is provided with inlet means to maintain the level of said non-conducting medium.
 7. The detection system of claim 2 wherein the fluid duct is hermetically sealed and the wick penetration is impermeable to the fluid stream so as to completely confine the fluid stream within the fluid duct. 